The present invention is directed to a separating closure liner and, in particular, a closure liner having an inner seal and a reusable liner separated by a light tack shearable adhesive.
In the food, pharmaceutical, household chemical, automotive, agricultural chemical, beverage and personal care product industry, plastic and glass containers are being used for product packaging. In order to preserve the product freshness and the integrity of the package, an inner seal material is utilized. This inner seal material, usually a disc having a diameter matching the diameter of the container opening, is sealed to the container neck opening by fusion, adhesive means or the like. Once the product is purchased by a consumer, the inner seal is removed in order to access the product.
Many times, the containers must be resealed since the product is not completely used by the consumer. In these instances, the closure for the container must be capable of forming a seal at the container opening to prevent spillage, loss of product freshness, etc. Often times, the container closure has a lining material therein which forms a gasket or seal between the container opening and the closure for sealing purposes.
The prior art has proposed seals which provide both the inner sealing function described above and a closure lining material for sealing the container after its initial opening. Typically, these prior art seals have four parts. Referring now to FIGS. 1A-1C, a typical prior art seal 1 is shown in an exemplary use with a closure 3 for a container 6.
In FIG. 1A, the seal 1 comprises a pulp board backing 5, a wax coating 7, an aluminum foil 9 and a heat sealable film or coating 11.
In use, the seal 1 is inserted into the closure 3 and the closure 3 is then applied and tightened to the container neck 13, see FIG. 1B. The thus tightened closure is then subjected to an induction field which heats the aluminum foil 9 so as to melt the heat sealable coating or film 11. This melting forms a seal 15 at the face 17 of the container neck 13.
During the induction heating of the aluminum foil, the wax layer 7 diffuses into the pulp board backing 5.
Referring now to FIG. 1C, once the closure 3 is removed from the container neck 13, the pulp board backing and wax coating is separated from the aluminum foil 9 and heat sealable coating or film 11. The diffusion of the wax coating 7 into the pulp board 5 permits the release or separation of the pulp board and wax laminate from the aluminum foil-heat sealable coating or film laminate.
Once the closure 3 is removed so that the seal 1 is now in the form of a two-part laminate, a consumer can peel away the aluminum foil to access the product within the container 6. With the aluminum foil 9 and heat sealable coating or film 11 removed, the closure 3 can be reinstalled on the container neck 13 with the pulp board backing forming a reusable seal.
Various types of materials have been proposed for the components of these types of prior art seals. The heat sealable coating or film 11 can be a material which is compatible with the material of the container 6.
The prior art seals discussed above are not without their disadvantages. The pulp board liner can be easily affected by the product inside the container since it readily absorbs moisture. The pulp board liner will also not pass a wash cycle during which both the closure and the container are being cleaned by washing with water.
The wax component of these prior art seals also can cause problems since it is sensitive to humidity and the time and energy used for induction sealing. The wax layer can also be sensitive to storage and/or shipping due to possible degradation over time. The wax/pulp board laminate also fails to provide a high degree of compressibility which can adversely affect resealability of the closure.
In view of the disadvantages noted above, a need has developed to provide an improved separating closure liner which overcomes the problems with prior art seals or liners. In response to this need, the present invention provides a separating closure liner which has improved compressibility and resiliency, is not sensitive to induction sealing parameters or degradation of properties over time, can be used in high temperature filling operations, is not sensitive to humidity, provides superior liquid and gas barriers and can be subjected to a conventional wash cycle without liner degradation.
Accordingly, it is a first object of the present invention to provide an improved separating closure liner.
Another object of the present invention is to provide a separating closure liner which utilizes a light tack shearable adhesive to facilitate separation of a reusable liner portion and an inner seal portion.
A further object of the present invention is to provide a separating closure liner which utilizes a polyolefin foam as part of the reusable liner portion.
A still further object of the present invention is to provide a separating liner which is torque sensitive.
Other objects and advantages of the present invention will become apparent as a description thereof proceeds.
In satisfaction of the foregoing objects and advantages, the present invention provides an improvement in separating closure liners which comprise a reusable liner portion and an inner seal portion, wherein the reusable liner portion is sized to fit within a closure for a container and the inner seal portion acts as a seal on an opening of the container. According to the invention, a light tack shearable adhesive is positioned between one face of the reusable liner portion and an opposing face of the inner seal portion. This light tack shearable adhesive permits separation between the reusable liner portion and the inner seal portion after the inner seal portion is attached to the container opening.
In another aspect of the invention, a polyolefin foam layer is included as part of the reusable liner portion of the separating closure liner.
In one embodiment, the light tack shearable adhesive can be in the form of a layer of constant thickness between the reusable liner portion and the inner seal portion. In an alternative embodiment, the light tack shearable adhesive can be in the shape of a discontinuous pattern so that the light tack shearable adhesive does not cover the entire face of either the reusable liner portion nor the inner seal portion. By controlling the amount or pattern of the light tack shearable adhesive between these two portions, the torque necessary to separate the reusable liner portion from the inner seal portion can be varied.
In another aspect of the invention, a layer of material is provided between the light tack shearable adhesive and the inner seal portion. This layer is designed to have a necessary surface energy to provide a bond between the inner seal portion and the reusable liner portion. The bond should be strong enough to take this laminated structure through the punching process (when individual liners are punched from the rolls of the product) and weak enough to provide a separation of the reusable portion from the inner seal portion when the inner seal portion is sealed to the container opening by the induction field applied thereto. This separating mechanism is completely different from prior art wax laminated products wherein the wax provides a strong initial bond which disappears when the foil is heated in an induction field whereby the wax melts into a liquid and the liquid wax is absorbed by the adjacent pulp board.
Besides including a polyolefin foamed layer, the reusable liner portion can include the combination of a polyolefin foamed layer and a non-foamed polyolefin layer. The reusable liner portion can also include a heat resistant polymeric layer disposed between the polyolefin foamed layer and the light tack shearable adhesive.
In a preferred embodiment, the inventive separating closure liner has the following laminate construction: a heat sealing or peelable adhesive layer for attachment to a container. A metal containing layer such as aluminum foil is then positioned next to the heat sealable layer. A paper is then positioned adjacent the foil layer. Adjacent the paper layer is a light tack shearable adhesive layer, either in a continuous or discontinuous pattern. Next to the light tack shearable adhesive material is a heat resistant polymer layer. A foamed polyolefin layer is positioned adjacent the heat resistant polymer. Permanent adhesives may be used to facilitate attachment between the metal-containing and the heat sealable film as well as the paper and metal-containing layer. A permanent adhesive can also be used to attach the heat resistant polymer layer to the foamed polyolefin layer.